Process of upgrading iron ore concentrates



l.. J. ERcK ETAL 3,067,957

PROCESS OF UPGRADlNG IRON ORE CONCETRATES Filed Sept. 8, 1959 Dec. 11, 1962 l @Marc A//rf/ M76@ uen-wf.

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United States Patent O 3,067,957 PROCESS F UPGRADING IRON ORE CONCENTRATES Louis J. Erck and Walter Nummela, Negauuee, Mich.,

assignors to The Cleveland-Cliffs Iron Company, Cleveland, Ohio, a corporation of Ohio Filed Sept. 8, 1959, Ser. No. 838,715

13 Claims. (Cl. 2in-23) This invention relates tothe art of ore benelication and is particularly concerned with a new method of upgradirt-g ore concentrates obtained from the flotation concentration of the low grade iron ore to an iron rich froth product.

Low grade iron ores have been converted into pulp containing as much as about 63% of iron by the conventional fatty acid froth concentrating method. Many prior efforts have been made to increase the iron content in such pulp. One of those efforts was to regrind the iron ore rich concentrate or pulp obtained 'from that process and to treat it again in a flotation cell. Another of those efforts was to add a silica depressor, such as sulfuric acid alone or with sodium tluosilicate, to the pulp before subjecting it to a second flotation treatment. Neither of these efforts, nor any other prior efforts with which we are familiar, has resulted in substantially increasing the iron content in the final product.

The present invention aims to upgrade substantially iron ore concentrates produced by the conventional flotation process and attains that aim by a new process which comprises a new combination of steps, some of which are new, which produces a new and unexpected result and which produces that result in a new way.

The present method invention will be better understood from the following specification taken in conjunction with the accompanying drawing which depicts the several steps and their sequential arrangement.

A conventional flotation process of making iron ore concentrates is shown in the upper part of the drawing where it is indicated that the run of mine ore is crushed, l

extremely ne particles are removed, a fatty acid ilotation reagent is added thereto and the mixture is subjected to treatment in a flotation cell,

In that cell an iron ore rich froth product is separated from the gangue rich product which is low in iron oxides. That froth product is known as the concentrate pulp and is usually filtered to remove most of the water.

In the step of grinding, the run of mine ore is reduced to particles less than about minus 35 mesh in size and the particles .smaller than abc-ut 15 microns referred to as slimes, are removed therefrom before the flotation agent is added and the pulp is treated in the flotation cell. Many of the conventional tlotation'agents or re- 3,067,957- v Patented Dec. 11, 1962 pelletizing of the material. That product has lheretofore been converted into pellets by being sintered and thereby hardened suciently to withstand the rough handling the pellets receive between the sintering machine and the blast furnaces and open hearth furnaces in which the ice pellets are to be used.

The present process combines the steps of that prior process with the additional steps of regrinding, heat conditioning and retreating the pulp in a flotation cell without adding any flotation reagent. The combination of these three steps is new and each of the heat conditioning and retlotation steps is new. As a result of combining the steps of the prior process with these new steps, a product is obtained from run of mine iron ore which contains from about 66% to about 69% or more of iron, or by applying these last three steps to the iron rich product of a flotation process, the iron content may be increased from as little as about 58% to as much as 66% to 69% or more.

The step of regrinding the iron ore rich froth product provides a material which contains between about 60% and about 80% of solids with from about 70% to about 90% of the particles being of about minus 325 mesh in size. This regrinding may be carried out on aqueous pulp or on the filter cake of the iron oxide rich product which has been repulped with water to the desired 60% to 80% solids consistency for the regrind. This regrinding may be applied to either of these materials as soon as it is produced or after aging for a short time. Preferably this aging time is not less than about one day or more than about three days but may be longer without any adverse results. Such aging apparently has the effect of increasing the recovery to a noticeable extent without any appreciable decrease in the grade of the product in the subsequent retreatment of the pulp in the flotation cell. Such agents which are resistant to heat may be used in the flotation cell. Preferably flotation agents are employed which include crude or distilled fatty acids or emulsied or saponifed fatty acids. Examples of such fatty acids which have been found to be particularly useful in this process consist of approximately equal parts of oleic and linoleic acids aggregating about 90% of the total agent, with the remainder thereof consisting of small amounts of each of saturated acids, rosin acids and unsaponiables. Examples of fatty acids having such compositions are Acintol Fatty Acids No. 1 and No. 2 sold by the Arizona Chemical Company and Pamak 1 and 4 sold by the Hercules Powder Company.

The iron ore rich froth product which comes from the flotation cell usually contains not less than 50% of iron and may, and frequently does, contain as much as, and possibly somewhat more than, 63% of iron. This iron rich frothproduct my require regrinding before pelletizing to some size such as is compatible with the art of aging apparently also has the effect of reducing the length of time that is required in the subsequent retreatment of the pulp in the flotation cell. It has been found that when from about to about 90% of the particles in the reground material have a size of about minus 325 mesh, substantilly all the iron values are liberated and also the material is better suited to pelletizing than is the larger size material. The process applies as well to an iron oxide rich froth product which is to be reground to a coarser or a finer size consist than 70% to 90% minus 325 mesh as would be determined by the compatibility with the pelletzing process.

The thus reground primary concentrate is then subjected to a heat conditioning treatment which has a marked effect on selective-separation of the iron ore from foreign materials in the succeeding reflotation step. This heat conditioning step is carried out in such a way that the temperature of the reground pulp is raised to between about F. and its apparent boiling temperature, which is about 210 AF. at sea level. Preferably the higher temperature is employed although with aged pulp, satisfactory upgrading occurs with temperatures in the lower part of the foregoing range. This heating may be carried out by direct cr indirect heating methods. As illustrative of th: direct heating method, it may be stated that high or low pressure steam may be injected directly into the pulp, or the hot product of combustion of liquid and gaseous fuels may be injected into the pulp. When such gases are used the apparent boiling temperature of the pulp is about 187 F. as contrasted with about 210 F. at sea level when steam is used. The reduction in the apparent boi'ing point of the pulp in direct heating with the hot combustion products is attributed to the partial pressures of the gases, such as nitrogen and carbon dioxide, exhausting from the bath along with the water vapor resulting in the boiling point commensurate with the partial pressure of the water vapor. Indirect heating of the pulp may be accomplished by means of a jacketed heat exchange unit or heating coils in which the pulp is brought into contact with the heating surface either by gent'e agitation or otherwise. It will be understood that such agitation is believed to be important mainly to keep the pulp in suspension and to provide such mixing action as an aid in the transfer of heat throughout the pulp. With the direct system of heating, agitation is preferred but may not be required.

When the reground pulp has been heated to the extent just described, water is added thereto for the purposes of the reotation treatment of the pulp in the flotation cell. Such water may be either hot water or even water at room temperature and lower. Apparently, the temperature of the added water has little effect on the upgrading of the pulp, provided of course that the pulp was properly heat conditioned, that is, raised to the requisite V temperature before the water was added thereto.

The reliotation step is carried out on the reground, heat conditioned pulp without adding any new flotation reagent thereto. It appears that a sufficient quantity of that reagent is retained by the pulp while it is being reground and heat conditioned for all needs of the reilotation step.

When the thus heat conditioned pulp is treated in the tiotation cell, the iron ore rich froth product which is obtained from that cell contains from about 66% to about 69% of iron. Apparently it makes little difference Whether the concentrates subjected to regrinding and heat conditioning steps contain as much as 61% to 63% of iron for substantially the same efficiencies may be obtained when iron ore pulp containing only about 58% of iron is subjected to the regrinding, heat conditioning and flotation retreatment steps.

The reason for the marked increase of iron in the iron rich product obtained from these new steps is not thoroughly understood. Undoubtedly, the regrinding step enhances liberation of iron oxide from gangue but such liberation would not account for the marked increase in iron content of the nal product. Also undoubtedly, the regrinding step exposes fresh mineral surfaces, both by breaking up particles containing iron oxide and gangue or breaking up iron oxide particles and also the scrubbing action of both newly exposed and previously exposed surfaces of iron oxides and also possibly of the slime coatings from the mineral particles in the pulp.

The heat conditioning treatment of the pulp apparently has a highly important effect in the upgrading of the pulp, but the reasons for this result are obscure. It may be that the higher temperature increases the solubility of the flotation reagent in the pulp and reduces the viscosity of the reagent itself and also reduces the viscosity of the pulp. These factors might tend to permit migration of the flotation reagent from one particle to another with the implication of reagent migration from fortuitously coated gangue to iron oxide particles. It may be that the heating action particularly when steam is used causes a cleansing action of the mineral surfaces from attached ions or slime particles. It may also be that the mineral surfaces are altered in some way, say as by hydration at the heat treating temperatures, with resultant change in their responses to the reflotation process. It is also possible that some of the unsaturated double bonds of say the oleic and linoleic acid molecules of the flotation reagent are oxidized during the aging or heat conditioning or both with the net result that the flotation reagent has become more effective in separating the iron oxides from the gangue. It is also possible that the otation reagent is structurally altered say as by the polymerization of the fatty acid molecules such as the oleic and linoleic acids. Whatever may be the theory as to the acton of the heat on the reground pulp and its content of liotation reagent, the fact is, as we have found, that the iron content in the final product is increased to a surprising and unforeseeable extent.

Although the extent of the increase in iron content which is traceable to each of the regrinding, heat conditioning and reflotation steps is not known exactly, it appears that the extent of such improvement which is traceable to the heat conditioning step is in excess of that traceable to each of the other two steps, acknowledging, of course, that the segregation of iron oxides from gangue is done in the reotation step.

It will be understood from the foregoing description that the present process may be carried out as a single, more or less continuous, process, that is, the pulp obtained from the first flotation step may be immediately reground and passed on through the heat conditioning and reliotation steps. Alternatively, the pulp produced by the notation step may be allowed to age from one to three days or more and then subjected to the regrinding, heat conditioning and retiotation steps. Thus, the invention may be considered as consisting of the combination of the steps of the conventional liotation process and the regrinding, heat conditioning and reflotation steps or as consisting of the combination of the regrinding, heat conditioning and reiiotation steps.

Having thus described this invention in such full, clear, concise and exact terms as to enable any person skilled in the art to which it pertains to make and use the same, and having set forth the best mode contemplated of carrying out this invention, we state that the subject matter which we regard as being our invention is particularly pointed out and distinctly claimed in what is claimed, it being understood that equivalents or modifications of, or substitutions for, parts of the above specifically described embodiment of the invention may be made without departing from the scope of the invention as set forth in what is claimed.

What is claimed is:

1. The method of making iron ore concentrates which comprises the steps of grinding an iron oxide ore to produce particles of a size less than about minus 35 mesh, conditioning such particles rwith a fatty acid flotation reagent, subjecting the thus conditioned material to treatment in a otation cell and separating the iron ore rich froth product from the gangue rich low iron product, regrinding the iron ore rich froth product to produce a pulp material, reconditioning such reground pulp by heating it to a temperature not less than about 140 F., subjecting such reground and reconditioned pulp in the presence of the reagent from the said conditioning step and added Water to treatment in a flotation cell, and separating the resulting iron ore rich froth product from the iron ore poor tailings.

2. The method of making iron ore concentrates which comprises the steps of grinding an iron oxide ore to produce particles of a size less than about minus 35 mesh, conditioning such particles with a fatty acid otation re agent, subjecting the thus conditioned material to treatment in a flotation cell and separating the iron ore rich froth product from the gangue rich low iron product, regrinding the iron ore rich froth product to produce a pulp material containing from about 70% to about 90% of particles having a size of about minus 325 mesh, reconditioning such reground pulp by heating it to a temperature of not less than about 140 F., subjecting such reground and reconditioned pulp to treatment in a flotation cell, and separating the resulting iron ore rich froth product from the iron ore poor tailings.

3. The method of making iron ore concentrates which comprises the steps of grinding an iron oxide ore to produce particles of a size less than about minus 35 mesh, conditioning such particles with a flotation reagent consisting of oleic and linoleic acids in approximately equal proportions aggregating about and the remainder consisting of small amounts of each of saturated fatty acids, rosin acids, and unsaponiable acids, subjecting the thus conditioned material to treatment in a otation cell and separating the iron ore rich froth product from the gangue rich low iron product, regrinding the iron ore rich froth product to produce a pulp material containing from about 70% to about'90% of particles having a size of about minus 325 mesh, reconditioning such reground pulpk by heating it to a temperature of not less than about 140 F., subjecting such reground and reconditionedpulp to treatment in a flotation cell, and separating the resulting iron ore rich froth product from the iron ore poor tailings.

4. The method of making iron ore concentrates which comprises the combination of the steps of grinding an iron oxide ore to produce particles of a size of less than about minus 35 mesh, desliming the thus ground ore and removing particles of less than about minus l5 microns, conditioning the remaining particles with a fatty acid flotation reagent, subjecting the thus conditioned material to treatment in a flotation cell and separating the iron ore rich froth product from the gangue rich low iron product, regrinding the iron ore rich froth product to product a pulp material containing from about 70% to about 90% of particles of about minus 325 mesh, heat conditioning such reground pulp by heating it to between about 140 F. and about the apparent boiling temperature of the pulp, subjecting such reground and heat conditioned pulp to treatment in a flotation cell, and separating the resulting iron ore rich froth product from the iron ore poor tailings.

5. The method of making iron ore concentrates which comprises the steps of grinding an iron oxide ore to produce particles of a size of less than about minus 35 mesh, desliming the thus ground ore and removing particles of less than about -15 microns, conditioning the remaining particles with a fatty acid flotation reagent, subjecting the thus conditioned material to treatment in a flotation cell and separating the iron ore rich froth product `from the gangue rich low iron product, regrinding the iron ore rich froth product to produce a pulp material containing about 75% of particles having a size of minus 325 mesh, reconditioning such reground pulp by heating it to between about 140 F. and about the apparent boiling temperature of the pulp, subjecting such reground and reconditioned pulp to treatment in a flotation cell, and separating the resulting iron ore froth product from the iron ore poor tailings.

6. The method of making iron ore concentrates which comprises the steps of grinding iron oxide ores to produce particles of a size of less than 4about minus 35 mesh, desliming the thus ground ore, conditioning -the remaining particles with a fatty acid flotation reagent, subjecting the thus conditioned material to treatment in a flotation cell and separating the iron ore rich froth product containing from about 50% to about 63% of iron from the gangue rich low iron product, regrinding the iron ore rich froth to produce a pulp material containing from about 70% to about 90% of particles having a size of about minus 325 mesh, reconditioning such reground pulp by heating it to the apparent boiling temperature of the pulp, subjecting such reground and reconditioned pulp to -treatment in a flotation cell, and separating thc resulting iron ore rich froth product from the iron ore poor tailings.

7. 'Ihe method of making iron ore concentrates which comprises the combination of the steps of grinding iron oxide ores to produce particles of a size of about minus 35 mesh, desliming the thus ground ore, conditioning the remaining particles with a fatty acid flotation reagent, subjecting the thus conditioned material to treatment in a flotation cell and separating the iron ore rich froth product from the gangue rich low iron product, aging said iron ore rich froth product for a period of time of not less than about one day, regrinding such iron ore rich froth product to produce a pulp material containing from about 70% to about 90% of particles of about minus 325 mesh, heat conditioning such reground pulp by heating it to between about 140 F. and about the apparent boiling temperature of the pulp, subjecting such reground and heat conditioned pulp to treatment in a flotation cell in the presence of added water and the flotation reagent retained in the reground and heat-conditioned pulp, and separating the resulting iron ore rich froth product from the iron ore poor tailings.

8. The method of increasing the iron content in an iron oxide ore rich froth product of flotation of the ore in a fatty acid reagent which comprises the steps of regrinding such iron ore rich froth product to produce a pulp material, heat conditioning such reground pulp by heating it to the apparent boiling temperature of the pulp, subjecting such reground and heat conditioned pulp to treatment in a notation cell in the presence of added water vand the reagent retained by the reground and heat-conditioned pulp, and separating the resulting iron ore rich froth product from the iron ore poor tailings.

9. The method of increasing the iron content in an iron oxide ore rich froth product of flotation of the ore in a fatty acid reagent which comprises the steps of regrinding such iron ore rich froth product to produce a pulp material, aging the pulp material for not less than about one day to increase the recovery appreciably and to decrease appreciably the time required for substantial completion of reotation, heat conditioning such reground pulp by heating it to the apparent boiling temperature of the pulp, subjecting such reground and heat conditioned pulp to treatment in a flotation cell in the presence of added water and the reagent retained by the reground and heat-conditioned pulp, and separating the resulting iron ore rich froth product from the iron ore poor tailings.

10. The method of increasing the iron content in an iron oxide ore rich product of flotation of the ore in a fatty acid reagent which comprises the steps of regrinding such iron ore rich froth product to produce a pulp material containing from about 70% to about 90% of particles of about minus A325 mesh, heat conditioning such reground pulp by heating it to the apparent boiling temperature of the pulp, subjecting such reground and heat conditioned pulp to treatment in a flotation cell in the presence of added water and the reagent retained by the reground and heat-conditioned pulp, and separating the resulting iron ore rich froth product from the iron ore poor tailings.

l1. The method of increasing the iron content in an iron oxide ore rich product of flotation of theore in a fatty acid reagent which comprises the steps of regrinding such iron ore rich froth product to produce a pulp material containing from about 70% to about 90% oi particles of about minus 325 mesh, aging the pulp material for not less than about one day, heat conditioning such reground pulp by heating it to the apparent boiling temperatureof the pulp, subjecting such reground and heat conditioned pulp to treatment in a flotation cell in the presence of added water and the reagent retained by the reground and heat-conditioned pulp, and separating the resulting iron ore rich froth product from the iron ore poor tailings.

12. 'I'he method of'increasing the iron content in an iron oxide ore rich fatty acid froth product of flotation of the ore in a fatty acid reagent which comprises the steps of regrinding such iron ore rich froth product to produce a plup material containing from about 70% te about of the particles of about minus 325 mesh, heat conditioning such reground pulp by heating it in the range of from about to the apparent boiling temperature, subjecting such reground and heat conditioned pulp to treatment in a fiotation cell in the presence of 'added water and the reagent retained by the reground and heatconditioned pulp, and separating the resulting iron ore rich froth product from the iron ore poor tailings.

13. The method of increasing the iron content in ar iron oxide ore rich fatty acid froth product of flotation ot the ore in a fatty acid reagent which comprises the step: of regrinding such iron ore rich froth product to produce a pulp material containing from about 70% to about 7 90% of the particles of about minus 325 mesh, aging the pulp material for between about one day and about three days, heat conditioning such reground pulp by heating it in the range of from about 140 F. to the apparent boiling temperature, subjecting such reground and heat conditioned pulp to treatment in a flotation cell in the presence of added water and the reagent retained by the reground and heat-conditioned pulp, and separating the resulting iron ore rich froth product from the iron ore poor tailings.

References Cited in the le of this patent UNITED STATES PATENTS 1,737,717 Handy Dec. 3, 1929 8 Weed Sept. 17, 1935 Booth Oct. 29, 1946 Dasher May 31, 1949 Wilson Apr. 10, 1956 McGarry Oct. 2l, 1957 Reerink et al. July 8, 1958 Bunge July 12, 1960 OTHER REFERENCES Canadian Mining and Metallurgical Bulletin, volume 5l, January-June 1958, pages 21S-218. 

8. THE METHOD OF INCREASING THE IRON CONTENT IN AN IRON OXIDE ORE RICH FROTH PRODUCT OF FLOTATION OF THE ORE IN A FATTY ACID REAGENT WHICH COMPRISES THE STEPS OF REGRINDING SUCH IRON ORE RICH FROTH PRODUCT TO PRODUCE A PULP MATERIAL, HEAT CONDITIONING SUCH REGROUND PULP BY HEATING IT TO THE APPARENT BOILING TEMPERATURE OF THE PULP, SUBJECTING SUCH REGROUND AND HEAT CONDITIONED PULP TO TREATMENT IN FLOTATION CELL IN THE PRESENCE OF ADDED WATER AND THE 